1. Field of Invention
The present invention relates to an oil passage construction which is provided for a die-cast formed product, and also to an oil passage construction for an internal combustion engine.
2. Description of Related Art
There is a type of internal combustion engine mounted to an automobile or the like in which oil is supplied, from an oil pressure path for supplying oil to a valve operating mechanism thereof, to a member which is attached to the exterior wall of the cylinder block or of a cam housing or the like for supporting the cam shaft. Such engines are disclosed in, for example, Japanese Patent Application Publication No. JP-A-2001-27109 and Japanese Patent Application Publication No. JP-A-2001-263015.
With an internal combustion engine such as those described above, oil passages are provided both to a member included in the internal combustion engine and to a member which is attached to the exterior thereof, in order to communicate these members with one another. Furthermore, as this type of externally attached member, there may be cited, for example, a timing chain of a cam shaft, an oil pressure type actuator of a variable valve operating mechanism, or the like. Or it would also be acceptable for this externally attached member to be some other type of appropriate auxiliary machinery.
For various components which make up an internal combustion engine, die-cast formed products are often employed, such as ones made from a light alloy material such as, for example, aluminum alloy or magnesium alloy or the like. As such die-cast formed products there may be cited, for example, a cam housing or a cylinder block or the like of the internal combustion engine.
By the way, during the manufacture of a die-cast formed product, generally, air or reaction gas is entrapped within one or more cavities in the formation mold. Due to this, minute voids termed blow holes can easily occur in the interior of the resulting die-cast formed product. However, with regard to the molded surface (for example the outer surface or the inner surface or the like) which contacts against the wall surface of the formation mold and along which the molten material which is being injected into the cavity in the formation mold is transferred, it is accepted that such blow holes cannot easily occur in its surface layer portion from its surface to a predetermined depth thereinto.
With the above described technique, if an oil passage which is to be provided in the member which is being manufactured as a die-cast formed product is formed by a cutting process, sometimes it happens that a blow hole becomes exposed upon the inner surface of this oil passage, which is undesirable. Due to this, during subsequent use of the die-cast formed product, the oil which is passing along this oil passage may permeate from this blow hole which is exposed upon the inner surface of this oil passage into a portion of the thickness of the die-cast formed product.
The situation has been investigated in which, for example, the surface of a member which is manufactured as such a die-cast formed product, such as a surface in which the opening of an oil passage is provided, is used as the mating face for an externally attached member of the type described above. For example, sometimes it is practiced to enhance the surface accuracy by eliminating the initially manufactured surface layer consisting of the above described molded surface by performing grinding finishing after the cutting process. Due to this finishing work, sometimes a portion of a blow hole becomes exposed upon the surface of the mating face, which is most undesirable.
If such a blow hole is present exposed upon the mating face surface, then there is possible that oil which has permeated from the oil passage into a thickness portion of the die-cast formed product may leak out from this surface to the exterior.